One suggestion (having also made one recently) is to source the cross pins first. They need to be high strength and at least 3mm (1/8") diameter to take the loads. It is annoying after cutting the slots to realise you can't find pins to fit them.
You are also wise to look for stainless wire of 0.9mm dia for clamp making. Heavier is annoyingly stiff to work with.
Built mine using 1/2 inch stainless steel tubing 6 inches long. The tapered end is a 1/2 inch SS bolt. The threaded part is a 3/8 inch SS carrage bolt 6 inches long. the pins are 1/8 inch SS roll pins, 1 1/2 inch long. The handle is Aluminum & there is a brass bushing between the handle & the tube. Ended up making 5 of them 1 for me & 4 for giveaways.
Here you go. This drawing is for the medium sized tool that I made. It works great, even with smaller wire, but you have to be careful using the small stuff, or the tool will break the wire. I made the body of mine from 303 stainless but just used plain old ready rod for the threaded portion. I never got around to making a fancy nut for mine either, I just used a stainless wingnut from the hardware store.
You can not tell the difference between yours and mince set next to each other. My first project I made on my new to me South Bend lathe and first lathe experience. BUT thinking I want to make the Stronghold haywire klamper.